1) I think favourable variance is always good for the organization because it shows always standard cost is higher than the actual cost and that always helps to make a profit for the organization. So, it's good always. 

2) Reasons for material price variance: unit of order: If a unit of order is more than our capacity then we need to purchase more materials than our standard or predetermined budget. The actual cost goes up with than standard cost of material and unfavourable variances will arise.

Rush order: If the order of products comes at a higher rate than our capacity then we need to purchase more material to make products or to meet the order than our standard or predetermined budget. If the actual cost goes up, then the standard cost of material and unfavourable variance will arise.

Quality of material purchase: If we purchase more quality material than our standard or budget then the actual cost goes up than the standard cost of material and unfavourable variance will arise.